Scientists have uncovered new clues about a curious fossil site in Nevada, a graveyard for dozens of giant marine reptiles. Instead of the site of a massive die-off as suspected, it might have been an ancient maternity ward where the creatures came to give birth, per the AP. The site is famous for its fossils from giant ichthyosaurs—reptiles that dominated the ancient seas and could grow up to the size of a school bus. Since the ichthyosaur bones in Nevada were excavated in the 1950s, many paleontologists have investigated how all these creatures could have died together. Now, researchers have proposed a different theory in a study published Monday in the journal Current Biology.
"Several lines of evidence all kind of point towards one argument here: That this was a place where giant ichthyosaurs came to give birth," said co-author Nicholas Pyenson, curator of fossil marine mammals at the Smithsonian National Museum of Natural History. Once a tropical sea, the site—part of Nevadas Berlin-Ichthyosaur State Park—now sits in a dry, dusty landscape, said lead author Randy Irmis, a paleontologist at the University of Utah. To get a better look at the massive skeletons, which boast vertebrae the size of dinner plates and bones from their flippers as thick as boulders, researchers used 3D scanning to create a detailed digital model, Irmis said. They identified fossils from at least 37 ichthyosaurs scattered around the area, dating back about 230 million years.
The bones were preserved in different rock layers, suggesting the creatures could have died hundreds of thousands of years apart, Pyenson said, adding a major break came when the researchers spotted some tiny bones among the adult fossils, and realized they belonged to embryos and newborns. The researchers concluded the creatures traveled to the site in groups for protection as they gave birth, like today's marine giants. The fossils are believed to be from the mothers and offspring that died there over the years. Other clues helped rule out some previous explanations. Testing the chemicals in the dirt didn't turn up any signs of environment shifts and the geology showed that the reptiles were preserved pretty far from the shore, making a mass beaching event unlikely, Irmis said. (Read more paleontology stories.)